The polishing of glass using cerium oxide (ceria) is well established and has a long history of use (see, for example, U.S. Pat. No. 2,383,500 and U.S. Pat. No. 2,816,824). Not only has ceria been used to shape glass into lenses, but it can also be used to polish the surface of the glass to chemically prepare it for the application of surface treatments (see, for example, Bartrug et al., U.S. Pat. No. 6,025,025 and Iversen et al., Patent Application Publication Pub. No. US 2009/0075093). In addition, ceria has been used to polish a variety of other silicon oxide surfaces both chemically and mechanically, for example photomask blanks, lithography optics and silicon wafers.
For final stage polishing applications, available ceria slurries typically have particle sizes small enough that they do not produce visible scratches. Particularly for high-performance applications, the particles are dispersed down to their primary size, do not contain higher-order agglomerates, and the dispersion of particles are stable (see, for example, P. G. Murray, “Nanocrystalline Cerium Oxide Improves Glass Polishing Operations” Photonics Spectra, August 2004). Examples of such high-performance ceria slurries include cerium oxide dispersions of NanoArc® Cerium Oxide nanopowder (Nanophase Technologies Corporation, Romeoville, Ill.; crystalline, non-porous, non-agglomerated particles having a mean particle size of 30 nm), such as NanoTek® CE-6040. The particles in the dispersion have a high zeta potential of 35-45 mV in the pH range of 3-4, and they form stable dispersions in water without additives (see, for example, Sarkas et al., U.S. Pat. No. 7,517,513).
Hydrophilic surface treatment of glass and other hard surfaces using silica sols is well established (see, for example, JP 01014129, issued 8 Jun. 1987, and Bindzil® CC product Brochure published by Eka/Akzo Nobel, April 2008). Not wishing to be bound by any particular theory, silica particles are present in a basic solution containing a volatile base, such as ammonia; as water, solvent and/or base evaporates, the silica particles coalesce and form a fully hydrated silicon oxide surface. The surface is very hydrophilic, and may be self-cleaning with ambient water, such as rain, which wets the surface and may remove dust and dirt. The use of silica and silicate hydrophilic surface treatments is advantageous in that no photoactivation is required in order achieve a hydrophilic effect, in contrast to analogous treatments based on titanium dioxide or titanium-substituted hydroxyapatite. In addition, a high degree of optical clarity is readily achieved using either silica or silicates, since these materials possess refractive indices very close to those of typical glass substrates, in contrast to titanium dioxide or titanium-substituted hydroxyapatite.
Stains on glass, particularly architectural glass, for example window glass in buildings, ships, and homes, are preferably removed before applying a surface treatment to the glass. The stains are often referred to as mineral or hard water stains. Compositions for removing mineral stains or hard water stains typically contain an abrasive and/or acid (see, for example, U.S. Pat. No. 3,425,870, U.S. Pat. No. 3,573,886 and U.S. Pat. No. 4,102,706). The acid present in some of these compositions includes mineral acids (such as hydrofluoric acid and hydrochloric acid) and/or organic acids.